Decoupling Electrochromism and Energy Storage for Flexible Quasi-Solid-State Aqueous Electrochromic Batteries with High Energy Density.

Currently, reported aqueous electrochromic batteries (ECBs) show only limited capacity with insufficient energy density and power density. Such a limitation is naturally imposed by the rationale that the cathode of ECBs stores charge by an ion intercalation/deintercalation mechanism, where the inherent inhibition of ion diffusion and structural collapse of cathode materials through repetitive charge/discharge cycles lead to low areal capacity and unsatisfactory electrochemical performance with short lifetime. Herein, we decouple the dual functions of electrochromism and energy storage in conventional cathodes of ECBs by introducing a polyaniline/triiodide composite cathode that is formed by direct electrolysis of an iodide-based quasi-solid-state aqueous electrolyte during charging.